The background information discussed below is presented to better illustrate the novelty and usefulness of the present invention. This background information is not admitted prior art.
Screw piling or screwpiles are a steel screw-in piling and ground anchoring system used for building foundations, pipeline tie-downs and in other applications. Screw pile(s), as used herein, includes screw piling, steel screw-in foundations, screw piers, helical piles, helical anchors, screw anchors, screw foundations and helical piers. They are often necessary for building foundations where the ground is not compacted, or strong enough or of variable capacity to carry a building structure. Screwpiles are typically manufactured using varying sizes of tubular hollow sections for the pile or anchor shaft. The pile shaft transfers a structure's load into the pile. Helical steel plates, or helixes, are welded to the pile shaft in accordance with the intended ground conditions.
To install screw piling, they are typically wound into the ground much like a screw into wood. Screw piles are preferably installed using earthmoving equipment or mobile machinery fitted with drive attachments which may include rotary drives, rotary drivers, powerheads or drive heads, see, for example, FIGS. 1a and 1b. The mobile machinery varies from skid-steer loaders to 5 ton through 30 ton excavators. Rotary drives, generally with torque capacities ranging from 5,000 Nm to 300,000 Nm, are custom fitted using various boom configurations. Drive attachments generally connect the screwpile to the machine. Likewise, hinged attachment means, such as a universal joint-type coupler, are often employed to suspend the rotary drive attachment from the boom of the mobile machinery; see, for example, FIG. 1b. One or more pivot pins may be utilized to connect the coupler to the boom and the drive attachment see, for example, the coupler disclosed in U.S. Pat. No. 6,942,430.
The level of torque that is required to turn the screw pile is indicative of the strength of the soil, and can be used to predict the capacity of the pile. Low installation torque indicates a weak soil and low pile capacity, whereas high installation torque indicates a relatively strong soil and greater pile capacity. Where the required installation torque can be accurately measured, the approximate holding capacity of a screw pile can be reliably predicted.
Traditionally, estimates of installation torque were made using hydraulic pressure gauges (to measure the amount of hydraulic pressure provided to a rotary drive), assumed or estimated gearbox ratios and compensation for any hydraulic motor losses. However, such estimates are fairly inaccurate and may not reliably predict a screw pile's holding capacity. As such, various devices and systems have been created to more accurately measure the installation torque of a screw pile.
One example is that by Pro-Dig, LLC of Kansas, U.S.A., which markets a screw pile torque monitoring system under the trade-mark INTELLI-TORK™. This system comprises a flanged member that mounts between the rotary drive and the screw piling and, therefore, rotates along with the screw piling as it is driven into the ground. As the rotary drive imparts torque to the screw piling, sensors in the flanged member measure this torque. Because this flanged member rotates along with screw piling it must send its measurements wirelessly to a display or recorder. As such, one disadvantage of this system is that such wireless signals may be subject to interference from the vibrations created during screw piling installation, especially as the screw piling is almost installed and the flanged member is driven closer to the ground.
A further disadvantage of this system is that the flanged member adds additional length to the rotary drive/screw pile assembly, thereby shortening the maximum length of screw pile that can potentially be installed using a particular mobile machinery. Yet a further disadvantage is that the INTELLI-TORK™ system also appears to be subject to interference from downward forces that may be applied by the mobile machinery as it pushes the rotary drive/screw pile assembly downwards during installation.
Another example is that by Russell Heale Engineering Pty Ltd of Burleigh Heads, Queensland, Australia, which markets a screw pile torque monitoring system under the trade-mark TORQATRON™. This system comprises a load cell member that mounts between the boom of the mobile machinery and the rotary drive. Unlike the flanged member of the INTELLI-TORK™ system, this load cell member does not rotate with the screw piling as it is driven into the ground (since it is mounted between above the rotary drive and to the boom). As such, wired connections can be used to transmit signals from the load/torque sensors in the TORQATRON™. However, this device and system does suffer from the other disadvantages present in the INTELLI-TORK™ system, namely that the load cell member adds additional length to the boom/rotary drive/screw pile assembly, thereby shortening the maximum length of screw pile that can potentially be installed using a particular mobile machinery that it also appears to be subject to interference from downward forces that may be applied by the mobile machinery as it pushes the boom/rotary drive/screw pile assembly downwards during installation.
Therefore, what is needed is a system and apparatus to measure the installation torque of a screw pile which is simple in design and does not have the above-mentioned disadvantages.